Coke production method

Abstract

To provide a means that presents a new indicator for a biomass-derived raw material replacing part of the coal used in the production of coke using a blast furnace and produces coke that has high strength even when a biomass-derived raw material has been blended with the coal. In the mass distribution of surface tension measured for the carbonized biomass blended with the coal blend for producing coke, the proportion of surface tension values equal to or greater than a lower limit value gammamin is 60 mass% or more of the whole, and the volatile content of the carbonized biomass on an anhydrous basis is 4.0 mass% or more.

Description

Coke manufacturing method

[0001] The present invention relates to a method for producing coke using biomass as part of the raw material.

[0002] Coke is a carbon-based lump product obtained by carbonizing coal. Blast furnace coke functions as a heat source and reducing agent, as well as a support material that ensures gas permeability and liquid permeability within the blast furnace. Therefore, the lump coke must have sufficient mechanical strength to ensure stable blast furnace operation.

[0003] To produce coke for blast furnaces, a coal blend containing multiple types of coal in a specified ratio is used. The coal blend is carbonized at a temperature of 1000°C or higher, either as is or after molding, to obtain coke in the form of a lump of coal bound together. High-strength coke can be obtained by using, as part of the coal blend, a type of coal known as caking coal, which has the property of easily softening and melting.

[0004] Two types of coal measurements have traditionally been used as indicators for managing coke strength. One is the average maximum reflectance of vitrinite (hereinafter referred to as "Ro"), as specified in Japanese Industrial Standards M 8816:1992, "Method for Measuring Microstructural Components and Reflectance of Coal." The higher the Ro value of coal, the higher the degree of carbonization and the stronger the coke matrix tends to be. The other is the maximum fluidity (hereinafter referred to as "MF") measured by a Gieseler Plastometer, as specified in Japanese Industrial Standards M 8801:2004, "Coals - Testing Methods." The higher the MF value of coal, the more likely it is to soften, melt, and flow when heated.

[0005] Patent Document 1, previously filed by the applicant, describes a new index used in selecting a combination of coal types to compose a coal blend: the measured surface tension of the powder obtained by heating coal to 500°C before blending, cooling it, and pulverizing it. According to this index, when coal powders with a small difference in weighted average values ​​of surface tension are combined, the strength of the resulting coke is higher than when coal powders with a large difference in weighted average values ​​of surface tension are combined.

[0006] In recent years, societal efforts to mitigate the impact of global warming by reducing emissions of carbon dioxide, a greenhouse gas, into the atmosphere have been accelerating. For this reason, studies are underway to replace a portion of the coal used as a coke raw material with carbon-neutral raw materials such as biomass. For example, Patent Document 2 describes a method for producing coke in which a woody biomass raw material heat-treated at temperatures above 300 to 400°C is mixed with coal and carbonized in a coke oven. Patent Document 3 also describes a method for producing highly reactive coke for blast furnaces in which biomass is heated to at least 1000°C or higher to pyrolyze it, and the resulting biomass char with a solid content of 1 mm or less in diameter is added to a coal blend.

[0007] International Publication No. 2013 / 145680 Japanese Patent Application Laid-Open No. 2005-272569 Japanese Patent Application Laid-Open No. 2014-77086

[0008] MC Williams and DW Fuerstenau, "A Simple Flotation Method for Rapidly Assessing the Hydrophobicity of Coal Particles", International Journal of Mineral Processing, Vol. 20, No. 1-2, Netherlands, June 1987, p.153-157.

[0009] When attempting to replace a portion of the coal used to make coke with a biomass-derived material, even a small substitution ratio can significantly reduce the strength of the resulting coke.

[0010] In the prior art, Ro and MF, which are effective as indicators for controlling the strength of coke, are both indicators that are assumed to be measured for coal. Therefore, even if attempts are made to measure Ro and MF for a sample consisting only of raw materials derived from biomass, the properties of coal and biomass are significantly different, so it is impossible to perform the measurements. Even if measurements can be performed, the measured values ​​are not appropriate for use as indicators for controlling the strength of coke containing raw materials derived from biomass.

[0011] Furthermore, the surface tension previously proposed by the applicant as a new index is based on a weighted average of the surface tensions measured individually for coals that soften and melt when heated to 500°C. However, biomass does not soften and melt when heated. Therefore, surface tension alone cannot be used as an index for managing the strength of coke containing biomass-derived raw materials. Therefore, a new index for managing the strength of coke containing biomass-derived raw materials is needed.

[0012] The present invention has been made in view of the above-mentioned problems, and its purpose is to present new indicators for biomass-derived raw materials that can replace a portion of the coal used in producing coke for blast furnaces, and to provide a means for producing high-strength coke even when biomass-derived raw materials are blended with coal.

[0013] In order to clarify the cause of the decrease in strength of coke that uses biomass as a part of the raw material, the inventors of the present patent application conducted detailed observations of defects present inside lumpy coke with decreased strength. As a result of the observations, it became clear that the interior of coke containing biomass-derived raw materials contains the following two main types of defects.

[0014] The first type of defect is a defect in which the softened and melted part of the coal does not fuse to the surface of the biomass-derived raw material, but the two are separated. The reason for the first type of defect is thought to be that while coal is prone to softening and melting during the temperature rise process of carbonization, the biomass-derived raw material is not carbonized and does not soften and melt.

[0015] The second type of defect is a crack caused by the destruction of raw materials derived from biomass. The cause of the second type of defect is thought to be a difference in the amount of shrinkage between the coal-derived portion and the biomass-derived portion during the shrinkage process after the thermoplastic coal resolidifies. Both the first and second type of defects can be the starting point for the progression of coke destruction. Therefore, to increase the strength of coke, it is necessary to minimize the occurrence of these defects.

[0016] The gist of the present invention, which was completed by the inventors based on the above observation results regarding defects present inside coke, is as follows.

[0017] [1] When producing coke by carbonizing a mixture obtained by blending a predetermined ratio of carbonized biomass produced by heat-treating biomass with a blended coal for coke production, the surface tension value is a lower limit value γ ｍｉｎ [2] The lower limit value γ of the surface tension is 60 mass % or more of the total, and the volatile content of the carbonized biomass is 4.0 mass % or more on a dry basis. ｍｉｎ is the mass average value γ in the mass distribution of the surface tension measured for a sample obtained by heating the blended coal to the thermoplastic temperature. ａｖｅ [3] The lower limit value γ of the surface tension is larger than ｍｉｎ The method for producing coke according to the above [1], wherein the lower limit γ of the surface tension is greater than 35.0±3.0 mN / m, which is the mass average value of the surface tension of a sample obtained by heating the coal blend to 450°C. ｍｉｎ is equal to 38.2 mN / m. [5] The method for producing coke according to any of [1] to [4] above, wherein a proportion of the carbonized biomass in the mixture is 1.0 mass% or more and 8.0 mass% or less. [6] The method for producing coke according to any of [1] to [5] above, wherein the biomass that is the raw material for the carbonized biomass includes at least one of palm kernel shells and woody biomass. [7] The method for producing coke according to any of [1] to [6] above, wherein the mass distribution of surface tension for the carbonized biomass is measured by a film flotation method. [8] The method for producing coke according to any of [1] to [7] above, wherein a proportion of particle sizes of 3.0 mm or less in the carbonized biomass is 70 mass% or more and a proportion of particle sizes of 3.0 mm or less in the blended coal is 70 mass% or more.

[0018] The present invention clarifies the properties of biomass-derived raw materials suitable for replacing a portion of the coal used in the production of coke for blast furnaces. As a result, it is possible to produce high-strength coke even when biomass-derived raw materials are blended with coal. Furthermore, it is possible to reduce carbon dioxide emissions derived from fossil fuels.

[0019] 1 is a graph showing the relationship between the heat treatment temperature and the surface tension of carbonized biomass in Examples. 2 is a graph showing the relationship between the heat treatment temperature and the volatile content of carbonized biomass in Examples.

[0020] Hereinafter, embodiments of the present invention will be described in detail.

[0021] In one embodiment, a method for producing coke according to the present invention includes the steps of: producing coke by carbonizing a mixture obtained by blending a coal blend for coke production with carbonized biomass produced by heat treating biomass in a predetermined ratio; and ｍｉｎ The carbonized biomass is characterized in that the proportion of carbonized biomass that is equal to or greater than 60 mass% of the total, and the volatile content of the carbonized biomass on a dry basis is 4.0 mass% or greater.

[0022] [Carbonized Biomass] In this embodiment, "biomass" refers to organic industrial resources derived from plants and animals that exist in the current ecosystem. The organic matter that constitutes biomass circulates within the ecosystem while changing its form. The carbon dioxide generated when biomass is burned originates from the carbon originally absorbed by living organisms when plants and animals grow, and therefore does not affect the increase or decrease in the total amount of carbon dioxide in the atmosphere, and is considered to be in a so-called carbon-neutral state. In contrast, the carbon dioxide generated when fossil fuels are burned originates from underground resources isolated from the current ecosystem, and is therefore not considered to be in a carbon-neutral state. Therefore, fossil fuels such as coal and oil are not included in biomass in this embodiment.

[0023] The biomass used in this embodiment may be any type of biomass that can be used as an industrial resource, including products produced in fields such as agriculture, forestry, livestock farming, and fisheries, as well as waste generated during production, as long as it satisfies the specified conditions described below. In a preferred embodiment, the biomass includes at least one of palm kernel shells and woody biomass. Palm kernel shells are biomass produced as a by-product after palm oil is extracted from palm kernels. Palm kernel shells are suitable for use in this embodiment because of their low cost and moderate strength. Examples of woody biomass include biomass made from wood from coniferous trees such as cedar, pine, and cypress, and broadleaf trees such as zelkova, birch, and eucalyptus. The part of the wood is not limited. Woody biomass also includes waste wood used in construction and papermaking, as well as unused parts such as thinned wood from forestry. Sawdust produced during lumber production is one of the most representative woody biomass materials.

[0024] The method for producing coke according to the present invention uses carbonized biomass produced by heat-treating biomass. In the heat treatment of biomass, the biomass is heat-treated in an air-tight atmosphere. By performing the heat treatment of biomass in an air-tight atmosphere, the progress of combustion of the biomass is hindered, and the biomass can be carbonized. To achieve an air-tight atmosphere, for example, a container is prepared that forms a space that prevents air from entering and through which an inert gas flows, and the biomass is loaded into the container and heat-treated.

[0025] The temperature for heat treating biomass may be adjusted appropriately depending on the type of biomass so that the surface tension and volatile content fall within suitable ranges. For example, when palm kernel shells are used as biomass, a temperature of 400°C or higher falls within a suitable range for the surface tension described below, and a temperature of 700°C or lower falls within a suitable range for the volatile content described below, so a temperature of 400°C or higher and 700°C or lower is preferred. Similarly, when cedar is used as biomass, a temperature of 500°C or higher and 800°C or lower is preferred. A higher temperature for heat treating biomass is more preferred from the viewpoint of surface tension, and a lower temperature is more preferred from the viewpoint of volatile content. In this specification, the term "heat treatment temperature" refers to the maximum temperature reached by biomass during heat treatment.

[0026] The time for heat treatment varies depending on the type of biomass and the mass of biomass to be heat treated at one time, but is preferably 1 minute or more and 60 minutes or less. A more preferred heat treatment time is 10 minutes or more. A more preferred heat treatment time is 30 minutes or less. In this specification, "heat treatment time" refers to the time from when the temperature of the biomass during heat treatment reaches the heat treatment temperature to when the heat treatment temperature is stopped being maintained.

[0027] The heat-treated biomass is converted into carbonized biomass during the heat treatment process. The particle size of the carbonized biomass is preferably 70% by mass or more and 100% by mass or less of particles of 3.0 mm or less, similar to that of blended coal used in ordinary coke production. If the proportion of particles of 3.0 mm or less is 70% by mass or more and 100% by mass or less, the carbonized biomass can be homogeneously mixed with the blended coal. A more preferred particle size range for the carbonized biomass is 100% by mass of particles of 3.0 mm or less. There is no lower limit for the particle size. In other words, the particle size may be any size as long as it is greater than 0 (zero).

[0028] When the proportion of particle sizes of 3.0 mm or less in the carbonized biomass is less than 70% by mass, the proportion of particle sizes of 3.0 mm or less can be adjusted to 70% by mass or more and 100% by mass or less by pulverizing the carbonized biomass. The particle size adjustment by pulverization may be performed on the biomass before heat treatment, on the carbonized biomass after heat treatment, or on both. A known pulverizer can be used to pulverize the biomass or carbonized biomass.

[0029] In this specification, "particle size" corresponds to the nominal mesh size of a test sieve as specified in Japanese Industrial Standards Z 8801-1:2019 "Test sieves - Part 1: Metal mesh sieves." In other words, powders and granular materials having a particle size larger than X mm are powders and granular materials that remain on a sieve with a nominal mesh size of X mm when sieved through a sieve. Powders and granular materials having a particle size of Y mm or less are powders and granular materials that fall below the sieve when sieved through a sieve with a nominal mesh size of Y mm.

[0030] When producing large amounts of carbonized biomass on an industrial scale, the yield can be increased and production costs can be reduced by omitting the steps of sieving or adjusting particle size by pulverization, or both. In this case, the proportion of particles with a particle size of 3.0 mm or less in the particle size distribution of the carbonized biomass based on mass is preferably 70 mass% or more. When particle size adjustment is not performed, the proportion of particles with a particle size of 3.0 mm or less is more preferably 80 mass% or more, and even more preferably 90 mass% or more. The upper limit of the proportion of particles with a particle size of 3.0 mm or less in the carbonized biomass is 100 mass%. The particle size distribution of the carbonized biomass based on mass can be determined by known methods, such as measuring the weight of powder or granules sieved using multiple sieves with different mesh sizes for a sample taken from the large amount of carbonized biomass produced, or irradiating the sample with a laser.

[0031] [Blending] In the coke production method according to this embodiment, a coke is produced by carbonizing a mixture obtained by blending a coal blend for coke production with carbonized biomass in a predetermined ratio. The coal blend may be any coal blend as long as it is suitable for coke production. A coal blend suitable for coke production refers to a coal blend from which high-strength coke can be produced by carbonizing only the coal blend as a raw material. Whether a coal blend is suitable for coke production can be predicted by measuring the Ro and MF values ​​of the coal blend.

[0032] The proportion of the coal blend for coke production having a particle size of 3.0 mm or less is preferably 70% by mass or more and 100% by mass or less. If the particle size of the coal blend is coarse, a property distribution will occur in coke production using a mixture of coal components, such as coals, with different properties. Therefore, it is preferable that the proportion of the coal blend having a particle size of 3.0 mm or less is 70% by mass or more. More preferably, the proportion of the coal blend having a particle size of 3.0 mm or less is 75% by mass or more. On the other hand, if the particle size is too fine, the bulk density of the coal blend charged into the coke oven will decrease, which may cause a decrease in coke strength. Therefore, the proportion of the coal blend having a particle size of 3.0 mm or less is preferably 90% by mass or less, and more preferably 85% by mass or less.

[0033] In a mixture obtained by blending carbonized biomass in a predetermined ratio with a coal blend for coke production, a significant effect in reducing carbon dioxide emissions can be obtained if the ratio of carbonized biomass in the mixture is 1.0% by mass or more, and the strength of the obtained coke is not significantly reduced if the ratio is 8.0% by mass or less, so the ratio of carbonized biomass is preferably 1.0% by mass or more and 8.0% by mass or less, and more preferably 2.0% by mass or more and 5.0% by mass or less.

[0034] In the coke manufacturing method according to the present invention, the mixture obtained by blending the blended coal and the carbonized biomass at a predetermined ratio may be sufficiently mixed without performing any special operation specifically for mixing. Specific examples of such cases include a case where the mixture conveyed by a belt conveyor falls onto the next belt conveyor, a case where the blended coal and the carbonized biomass are blended and then pulverized using pulverization equipment, and a case where the moisture content is adjusted while stirring the blended coal and the carbonized biomass using coal moisture control equipment. These cases are preferable because they can reduce the equipment and costs required for mixing.

[0035] In the mixture, it is preferable that the blended coal and the carbonized biomass are uniformly mixed. This can prevent the problem of the carbonized biomass, which does not soften or melt when heated, being unevenly distributed in one place and remaining unsolidified after the carbonization process. If mixing is insufficient, a coal mixer can be used to mix the blended coal and the carbonized biomass. As the coal mixer, for example, a mixer that mainly performs convective mixing, a mixer that mainly performs shear mixing, or a mixer that performs a combination of convective and shear mixing can be used. Here, convective mixing refers to mixing that mainly involves convection and diffusion of the sample, and shear mixing refers to mixing that involves shearing, collision, grinding, etc. of the sample.

[0036] In the coke production method according to the present embodiment, coke is produced by carbonizing a mixture obtained by blending a coal blend for coke production with carbonized biomass at a predetermined ratio. The mixture is charged into a coke oven and carbonized by heating in an air-tight atmosphere.

[0037] If the carbonization temperature is 900°C or higher, coke of sufficient strength can be obtained. 950°C or higher is more preferable. On the other hand, if the carbonization temperature exceeds 1250°C, not only will a huge amount of energy be required for heating, but thermal decomposition of the coke may occur, resulting in a decrease in strength. Therefore, the carbonization temperature is preferably 1250°C or lower, and more preferably 1100°C or lower. The carbonization temperature refers to the maximum temperature reached by the mixture during carbonization.

[0038] [Surface tension] In the coke manufacturing method according to the present embodiment, in the mass distribution of the surface tension measured for the carbonized biomass, the surface tension value is set to a lower limit value γ ｍｉｎ The proportion of carbonized biomass that is equal to or greater than this is 60 mass % or greater of the total.

[0039] Carbonized biomass is not a substance with a single component and structure, but varies in the degree of carbon concentration, molecular weight of constituent molecules, content of volatile matter, etc. depending on the region. For this reason, the surface tension of carbonized biomass cannot be determined to a single value, but has a distribution. Therefore, in this embodiment, the mass distribution of surface tension is first determined for the carbonized biomass obtained by heat treatment. In this specification, "mass distribution of surface tension" refers to a graph in which the horizontal axis represents the surface tension measured for an aggregate of carbonized biomass powder, and the vertical axis represents the mass or cumulative mass of powder for each division. A specific method for measuring the mass distribution of surface tension will be described later. Next, in the determined mass distribution of surface tension of the carbonized biomass, the surface tension value is calculated by subtracting the predetermined lower limit value γ ｍｉｎ Only carbonized biomass in which the proportion of carbonized biomass having a surface tension value equal to or greater than the lower limit value γ is selected and used. ｍｉｎ The conditions for the heat treatment of the biomass may be adjusted so that the above proportion is 60 mass % or more of the total. By using carbonized biomass that satisfies these conditions, it is possible to produce coke with high strength.

[0040] In this embodiment, the suitability of use is not determined based on a single representative value such as a weighted average value derived from the distribution of surface tension of carbonized biomass, but rather based on the mass distribution of surface tension, where the surface tension value is the lower limit value γ ｍｉｎ Only carbonized biomass in which the proportion of the surface tension or more is 60 mass % or more of the total is used. This makes it possible to accurately determine whether or not carbonized biomass with a wide range of surface tension values ​​can be used. In a preferred embodiment, the surface tension value is less than the lower limit γ ｍｉｎ The proportion of the above is preferably 70% by mass or more of the total, and more preferably 80% by mass or more.ｍｉｎ The upper limit of the above proportions is 100% by mass of the total.

[0041] The lower limit value γ of the surface tension in this embodiment ｍｉｎ is set in advance to the lower limit value γ ｍｉｎ The strength of the coke obtained by carbonization of each type of carbonized biomass is examined by preparing multiple types of carbonized biomass with different carbonization ratios, blending each type of carbonized biomass with blended coal, and then carbonizing the blended coal.

[0042] Although the details of why high-strength coke can be produced by using carbonized biomass with adjusted surface tension according to the present embodiment are unclear, it is believed that the following reason is likely. As mentioned above, Patent Document 1 describes that when coals with similar weighted average values ​​of surface tension are combined, the strength of the resulting coke is higher than when coals with a large difference in weighted average values ​​of surface tension are combined. This means that, with regard to adhesion between coals, the smaller the difference in surface tension, i.e., the magnitude of interfacial tension, the stronger the bond between the coal blend. In contrast, carbonized biomass is a raw material that does not undergo thermoplasticity like coal. Therefore, when considering the adhesion phenomenon at the interface between coal and carbonized biomass, a different approach is required than the conventional approach to adhesion between coals.

[0043] Generally, when the surface tension of a solid is greater than that of a liquid at the interface between a solid and a liquid, the liquid can wet the surface of the solid. If this is the case, when the surface tension of the carbonized biomass, which is solid, is greater than that of the thermoplastic blended coal, which is liquid, the thermoplastic blended coal can wet and spread on the surface of the carbonized biomass in the carbonization step, which is considered to result in an increase in the strength of the obtained coke. The lower limit value γ of the surface tension in this embodiment is ｍｉｎ is determined experimentally or based on the surface tension of the blended coal, and 60 mass % or more of the carbonized biomass is below the lower limit γ ｍｉｎBy ensuring that the surface tension is equal to or greater than this, wetting occurs at many locations in the mixture, which is believed to prevent the occurrence of type 1 defects in which the blended coal and the carbonized biomass are separated, and as a result, coke with high strength can be produced.

[0044] To determine the mass distribution of surface tension for carbonized biomass, it is preferable to use the film flotation method described in Non-Patent Document 1. The film flotation method makes it possible to determine the surface tension distribution based on the mass of powder for an aggregate of powders that has a distribution in the magnitude of surface tension, using a relatively simple procedure. The measurement of the mass distribution of surface tension using the film flotation method is outlined below.

[0045] The film flotation method utilizes the property that when powder particles floating on the surface of a liquid with a known surface tension begin to settle, the surface tension of the powder is equal to the surface tension of the liquid. First, multiple liquids with different surface tensions are prepared. The surface tensions of the liquids are selected to cover the range of surface tension values ​​of the powder to be measured. For example, when an aqueous solution of ethanol is used as the liquid, the surface tension of ethanol at 20°C is 22.6 mN / m, and the surface tension of pure water is 72.8 mN / m. Therefore, by adjusting the concentration of ethanol, a liquid with a surface tension of 22.6 mN / m or more and 72.8 mN / m or less can be prepared.

[0046] The number of sections of the surface tension mass distribution to be calculated is determined by the number of types of liquid prepared. In the present application, the number of types of liquid is not particularly limited, but a number of types of liquid of 5 or more increases the measurement accuracy, while a number of types of liquid of 20 or less allows the measurement to be completed in a short time, so it is preferable that the number of sections is 5 or more and 20 or less. A more preferable lower limit of the range of the number of sections is 8 or more. A more preferable upper limit of the number of sections is 15 or less. It is also preferable that the difference in surface tension between the liquids is as equal as possible.

[0047] Next, the particle size of the carbonized biomass sample to be used for the measurement is adjusted. If the particle size of the sample is 53 μm or more, the sample is less likely to aggregate, and if it is 150 μm or less, the effect of gravity can be ignored. Therefore, it is preferable that the particle size of the sample is 53 μm or more and 150 μm or less.

[0048] Next, the mass of the carbonized biomass sample with adjusted particle size is measured, and then it is sprayed onto the surface of the prepared liquid. After a period of time, the sample that has not settled but is floating on the surface of the liquid is collected, its mass after drying is measured, and its ratio to the mass of the sample before spraying is calculated. This calculated value indicates the proportion of samples with a surface tension smaller than that of the liquid. By repeating this series of procedures for all liquids, the mass distribution of surface tension can be determined. Note that the surface tension value of a liquid is usually measured at 20°C, so it is preferable to control the temperature of the liquid when spraying the carbonized biomass sample to 20°C.

[0049] As described above, the mass distribution of surface tension can be expressed by a graph with the surface tension on the horizontal axis and the mass or cumulative mass of powder for each category on the vertical axis. ｍｉｎ The percentage of samples that are equal to or greater than the lower limit can be calculated as the total area above the lower limit in the frequency distribution graph, or as the difference between the reading at the lower limit and 100% in the cumulative frequency graph. ｍｉｎ When is midway between the surface tension segments, the graph reading at the midpoint can be estimated by interpolating between the adjacent values.

[0050] The mass distribution of surface tension measured by the above method shifts in the direction of increasing the surface tension value as the heat treatment temperature of the biomass in the carbonization process increases. This is thought to be because the higher the treatment temperature of the biomass, the more the carbonization of the biomass progresses, and the surface properties of the carbonized biomass change in the direction of increasing the surface tension. Therefore, in the mass distribution of surface tension measured for the carbonized biomass, when the surface tension value is below the lower limit value γ ｍｉｎ If the proportion of samples with a surface tension of 100% or more is less than 60% by mass, the heat treatment temperature of the biomass in the carbonization step should be changed to a higher temperature so that the surface tension value does not exceed the lower limit γ ｍｉｎThe proportion of the samples having this or higher content may be adjusted to 60% by mass or more of the total.

[0051] In a preferred embodiment, the lower limit value γ of the surface tension ｍｉｎ The mass average value γ in the mass distribution of surface tension measured for a sample obtained by heating a blended coal to its thermoplastic temperature ａｖｅ As mentioned above, the wettability between the coal blend and the carbonized biomass becomes an issue when the mixture is heated to the thermoplastic temperature of the coal blend in the carbonization process. It is generally believed that the coal blend softens and melts in a temperature range of 350°C or higher and 550°C or lower. Therefore, theoretically, if the surface tension of the carbonized biomass is higher than the surface tension of the coal blend in this temperature range, the wettability between the two is considered to be good. However, as mentioned above, the film flotation method uses a liquid at 20°C, and therefore, there is no known means for measuring the mass distribution of surface tension in situ in a temperature range of 350°C or higher.

[0052] Therefore, in a preferred embodiment, instead of measuring the surface tension of a coal blend in situ at the thermoplastic temperature, the mass distribution of the surface tension of a sample obtained by heating the coal blend to the thermoplastic temperature is measured using a liquid at 20°C, and the mass average value (weighted average) γ ａｖｅ Then, the lower limit value of the surface tension for carbonized biomass, γ ｍｉｎ is the mass average value γ ａｖｅ This sets the lower limit of the surface tension γ ｍｉｎ Rather than being experimentally determined by trial and error, it can be determined in fewer steps based on reasonably obtained measurements.

[0053] The reason why the measured value of surface tension measured at 20°C serves as an indicator of wettability in the temperature range of 350°C or higher and 550°C or lower, where the surface of a coal blend softens and melts, is as follows. In a sample obtained by heating a coal blend to its softening temperature, the chemical components of the material change to such an extent that the measured value of surface tension changes due to the softening and melting of the coal. These changes remain in the coal blend as thermal history, and the changed state is maintained even after it is cooled to 20°C. Therefore, it is thought that the measured value of surface tension measured at 20°C reflects the change in state when heated to the softening and melting temperature. Similarly, it is thought that the thermal history of heat-treated carbonized biomass at the heat treatment temperature is reflected in the measured value of surface tension measured at 20°C.

[0054] In a preferred embodiment, the lower limit value γ of the surface tension ｍｉｎ is greater than 35.0±3.0 mN / m, which is the mass average value in the mass distribution of surface tension measured for a sample obtained by heating a coal blend to 450°C. When the fluidity of coal used in coke production is measured using a Gieseler plastometer, many coals exhibit a maximum value (MF) around 450°C. In other words, from the viewpoint of fluidity, coal thermoplasticity is considered to be most advanced at 450°C. Therefore, in this preferred embodiment, 450°C is used to represent the temperature at which the coal blend thermoplasticity occurs.

[0055] In order to measure the surface tension of a coal blend, several types of coal with different origins and grades were carbonized up to 450°C in an inert gas atmosphere to obtain semi-coke. The mass distribution of the surface tension of the obtained semi-coke was measured by a film flotation method, and the mass average value was calculated, which was in the range of 35.0±3.0 mN / m. Therefore, in this preferred embodiment, the lower limit value γ of the surface tension is ｍｉｎ is set to a value greater than 35.0±3.0 mN / m. Since the surface tension of semi-coke varies within a range of ±3.0 mN / m, the lower limit of the surface tension γ ｍｉｎ It is more preferable to set the lower limit of the surface tension γ to a value greater than 38.0 mN / m. ｍｉｎis preferably set to a value of 40.0 mN / m or less.

[0056] In a preferred embodiment, the lower limit value γ of the surface tension ｍｉｎ is equal to 38.2 mN / m. The surface tension of a water (80%)-ethanol (20%) mixed solution at 20°C is 38.2 mN / m. This value happens to be larger than 38 mN / m. In addition, a water (80%)-ethanol (20%) mixed solution can be easily prepared. Therefore, the lower limit value γ of the surface tension in this preferred embodiment is ｍｉｎ The value is set to 38.2 mN / m.

[0057] In this preferred embodiment, instead of determining the mass distribution of surface tension in the film flotation method, the surface tension measurement can be simplified by using only one liquid: a water (80%)-ethanol (20%) mixed solution. Specifically, a carbonized biomass sample whose particle size has been adjusted using the above method is sprayed onto the surface of a water (80%)-ethanol (20%) mixed solution at 20°C. After a period of time, the sample that has not settled but is floating on the surface is collected and its mass after drying is measured. The mass of the settled sample is calculated by subtracting the mass of the floating sample from the mass of the sample before spraying. Since the surface tension value of the settled sample is 38.2 mN / m or greater, the surface tension requirement of the present invention is met if the proportion of the settled sample is 60 mass% or greater.

[0058] [Volatile content] In the coke production method according to this embodiment, the volatile content of the carbonized biomass is 4.0% by mass or more on a dry basis. Analysis of the volatile content of the carbonized biomass in this embodiment is performed in accordance with the method specified in Japanese Industrial Standards M 8812:2004 "Coals and cokes - Industrial analysis methods." By using the volatile content on a dry basis, the volatile content can be appropriately controlled even if moisture subsequently adheres to the carbonized biomass.

[0059] In this embodiment, the volatile content of carbonized biomass is analyzed, and only carbonized biomass with a volatile content of 4.0% by mass or more is selected, and only the selected carbonized biomass is used. Alternatively, the conditions for the heat treatment of biomass may be adjusted so that the volatile content is 4.0% by mass or more. By using carbonized biomass with a volatile content of 4.0% by mass or more, high-strength coke can be produced. In a preferred embodiment, the volatile content of the carbonized biomass on an anhydrous basis is 5.0% by mass or more.

[0060] Although the details of why high-strength coke can be produced by using carbonized biomass with a volatile content of 4.0% by mass or more according to this embodiment are unclear, it is believed that the reason is likely as follows: In the process of producing coke by carbonizing coal, the coal softens and melts at temperatures above 300°C, adhering to each other, and then solidifies again at temperatures above 500°C, becoming a solid as a whole. When the coal is then heated to 1000°C, contraction occurs as the volatiles contained in the coal are released. In this process, it is believed that the more volatiles contained in the coal, the greater the amount of contraction of the coal due to the release of volatiles. Similarly, it is believed that the more volatiles contained in the carbonized biomass, the greater the amount of contraction of the carbonized biomass due to the release of volatiles.

[0061] As described above, defects (type 2 defects) consisting of cracks caused by destruction of the biomass-derived raw material portions are present inside coke containing biomass-derived raw materials. The cause of these defects is thought to be the difference in the amount of shrinkage between the coal-derived portion and the biomass-derived portion during the shrinkage process after the thermoplastic coal resolidifies. It is presumed that when the volatile content of the carbonized biomass is less than 4.0% by mass, the carbonized biomass-derived portion barely shrinks, while the surrounding blended coal-derived portion shrinks, resulting in stress being applied to the carbonized biomass-derived portion and cracking. In this embodiment, since the volatile content of the carbonized biomass is 4.0% by mass or more, the carbonized biomass-derived portion and the surrounding blended coal-derived portion shrink to the same extent, which is thought to prevent the occurrence of type 2 defects.

[0062] The amount of volatile matter contained in carbonized biomass decreases as the heat treatment temperature of biomass in the carbonization process increases. This is thought to be because the higher the treatment temperature of biomass, the more volatile matter is released from the biomass. Therefore, if the volatile matter measured for carbonized biomass is less than 4.0% by mass, the heat treatment temperature of the biomass can be changed to a lower temperature to adjust the volatile matter to 4.0% by mass or more. In addition to changing the heat treatment temperature, the volatile matter can also be adjusted by changing the heat treatment time, changing the type of biomass used, etc. Of these methods, changing the heat treatment temperature is preferred because it is easy to control.

[0063] In the coke manufacturing method according to this embodiment, the lower limit of the volatile content of the carbonized biomass on a dry basis is set to 4.0 mass% or more, but the upper limit is not particularly specified. However, when the volatile content is adjusted by changing the heat treatment temperature of the biomass in the carbonization step, as described above, the lower the heat treatment temperature of the biomass in the carbonization step, the lower the surface tension value. Therefore, when the surface tension value is lower than the lower limit γ ｍｉｎ The heat treatment temperature cannot be lowered until the cumulative mass of the carbonized biomass, which is equal to or greater than 60 mass%, becomes less than 60 mass% of the total. Taking this into consideration, it is preferable that the volatile content does not exceed 35 mass%.

[0064] As described above, in this embodiment, high-strength coke can be produced by using carbonized biomass whose surface tension and volatile content fall within predetermined ranges. The heat treatment conditions that bring the surface tension and volatile content within the predetermined ranges vary significantly depending on the type of biomass used. Therefore, it is preferable to determine the heat treatment conditions individually for each type of biomass used. Among the heat treatment conditions, the temperature varies depending on the type of biomass and other heat treatment conditions, but in many cases, the surface tension and volatile content can be adjusted to fall within the ranges of this embodiment by performing heat treatment at a temperature of approximately 400°C or higher and 800°C or lower.

[0065] [Strength Evaluation] The effects of the present invention can be confirmed by evaluating the strength of the coke obtained by the coke manufacturing method according to this embodiment. There are various methods for evaluating coke strength, but the method of evaluating rotational strength by the drum method specified in Japanese Industrial Standards K 2151:2004, "Cokes - Test Methods," is a test that simulates the generation of dust from coke, which is a problem when used in a blast furnace. This method is currently the most widely used in Japan, and is therefore preferred. The drum method involves inserting a sample into a specified drum testing machine, rotating it at a specified speed for a specified number of rotations, sieving it through a specified sieve, determining the mass of each classification, and expressing the added percentage (%) of the sample as the drum strength index (symbol: DI).

[0066] As will be described later, in the examples of this specification, the drum rotation speed was set to 150 rpm, and the ratio of the mass of coke that did not pass through a sieve with a 15 mm mesh size after rotation to the mass of coke inserted into the drum testing machine was defined as the drum strength index (%). The drum strength index indicates the mass ratio of coke that was not crushed to a size of 15 mm or less even after rotation in the drum testing machine. A larger DI value indicates higher coke strength.

[0067] Examples of the present invention will be described below. Note that the embodiments of the present invention are not limited to the following examples, and the embodiments of the present invention can be modified as desired without departing from the gist of the present invention.

[0068] A coal blend with an Ro of 1.0% and a common logarithm of MF (log(MF / ddpm)) of 2.5 was prepared. This coal blend was pulverized to produce a coal blend in which the proportion of particles with a particle size of 3.0 mm or less was adjusted to 100% by mass. Two types of biomass, palm kernel shells and cedar, were prepared. These biomasses were individually heat-treated in an air-tight atmosphere at biomass temperatures of 400°C, 500°C, 700°C, 800°C, or 900°C to obtain carbonized biomass. These carbonized biomasses were pulverized to produce carbonized biomass samples in which the proportion of particles with a particle size of 3.0 mm or less was adjusted to 100% by mass. For the obtained carbonized biomass samples, the mass proportion of samples with a surface tension of 38.2 mN / m or more was measured using a water (80%)-ethanol (20%) mixed solution at 20°C, and the volatile content on an anhydrous basis was also measured. The measured values ​​are shown in Table 1. The change in the mass ratio of samples with a surface tension of 38.2 mN / m or more versus the heat treatment temperature is shown in FIG. 1, and the change in the volatile content on an anhydrous basis is shown in FIG.

[0069]

[0070] According to the above measurement results, the higher the heat treatment temperature of the carbonized biomass, the greater the mass proportion of samples with a surface tension of 38.2 mN / m or more and the lower the volatile content. The heat treatment temperatures at which the proportion of samples with a surface tension of 38.2 mN / m or more was 60 mass% or more and the volatile content was 4.0 mass% or more were in the range of 400°C or more and 700°C or less for palm kernel shells, and 500°C or more and 800°C or less for cedar.

[0071] Next, the blended coal and the carbonized biomass were blended so that the blending ratio of the carbonized biomass in the mixture was 2.0%, 4.0%, or 5.0%, and the moisture content was adjusted to 8.0 mass%. 16 kg of each mixture was prepared for each type of carbonized biomass. This mixture was filled into a stainless steel container, inserted into an electric furnace through which nitrogen gas was circulated, heated, and carbonized. The bulk density of the mixture in the container was 775 kg / m on an anhydrous basis. ３The container filled with the mixture was charged into an electric furnace set at a furnace wall temperature of 1,050°C, and carbonization was performed while maintaining the furnace wall temperature for 6 hours from the time of charging. After that, the container was transferred to a cooling facility through which room-temperature nitrogen gas was circulating and cooled, thereby obtaining a coke containing biomass as a raw material. In addition, to compare the drum rotation strength, only the same blended coal was carbonized under the same conditions to obtain a coke containing no biomass as a raw material. Next, the drum strength index (DI) of the obtained coke was measured under conditions of a drum rotation speed of 150 rpm and a sieve opening of 15 mm. The measured DI of the base without carbonized biomass was 79.1. The difference ΔDI between the obtained measurement value and the drum strength index of a coke containing no biomass as a raw material was calculated. The calculated ΔDI values ​​are shown in Table 2.

[0072]

[0073] According to Tables 1 and 2, the ΔDI values ​​of the cokes of Examples 1 to 9, which were made from mixtures containing carbonized biomass that satisfied the surface tension and volatile content ranges of the present invention, did not decrease by more than -2.0%. If the ΔDI does not decrease by more than -2.0%, the strength of the coke can be adjusted by adjusting the quality of the coal blend and the production conditions, and therefore the level is considered to be acceptable for practical use. On the other hand, the cokes of Comparative Examples 1 to 6, which had surface tensions or volatile content outside the ranges of the present invention, showed a significant decrease in drum rotation strength. These facts demonstrate that the coke production method of the present invention can produce coke with higher strength based on more reliable predictions than conventional techniques.

[0074] According to the coke manufacturing method of the present invention, it is possible to produce coke with high strength that can withstand use in a blast furnace, even when part of the coal that is the raw material for the coke is replaced with a raw material derived from biomass.

Claims

1. When producing coke by carbonizing a mixture obtained by blending a predetermined ratio of carbonized biomass produced by heat-treating biomass with blended coal for coke production, the surface tension value is a lower limit value γ ｍｉｎ the proportion of the carbonized biomass or more is 60 mass% or more of the total, and the volatile content of the carbonized biomass is 4.0 mass% or more on a dry basis.

2. The lower limit of surface tension γ ｍｉｎ is the mass average value γ in the mass distribution of the surface tension measured for a sample obtained by heating the blended coal to its thermoplastic temperature. ａｖｅ The method for producing coke according to claim 1 , wherein the coke content is greater than or equal to 100%.

3. The lower limit of surface tension γ ｍｉｎ The method for producing coke according to claim 1 , wherein the mass average value of the surface tension of a sample obtained by heating the blended coal to 450° C. is greater than 35.0±3.0 mN / m, which is a mass average value in a mass distribution of the surface tension measured for a sample obtained by heating the blended coal to 450° C.

4. The lower limit of surface tension γ ｍｉｎ The method of claim 1 , wherein the tensile strength of the coke is equal to 38.2 mN / m.

5. A method for producing coke according to any one of claims 1 to 4, wherein the ratio of the carbonized biomass in the mixture is 1.0 mass% or more and 8.0 mass% or less.

6. The method for producing coke according to any one of claims 1 to 5, wherein the biomass that is the raw material for the carbonized biomass includes at least one of palm kernel shells and woody biomass.

7. The method for producing coke according to any one of claims 1 to 6, wherein the measurement of the mass distribution of surface tension for the carbonized biomass is carried out by a film flotation method.

8. A method for producing coke according to any one of claims 1 to 7, wherein the proportion of particles in the carbonized biomass having a particle size of 3.0 mm or less is 70 mass% or more, and the proportion of particles in the blended coal having a particle size of 3.0 mm or less is 70 mass% or more.

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